The present invention is in the field of hazardous waste control and more particularly relates to the control and reliable containment of flow of materials in the Earth.
Toxic substance migration in the Earth poses an increasing threat to the environment, and particularly to ground water supplies. Such toxic substance migration may originate from a number of sources, such as surface spills (e.g., oil, gasoline, pesticides, and the like), discarded chemicals (e.g., PCB's, heavy metals), nuclear accident and nuclear waste (e.g., radioactive isotopes, such as strontium 90, uranium 235), and commercial and residential waste (e.g., PCB's, solvents, methane gas). The entry of such hazardous materials into the ecosystem, and particularly the aquifer system, is well known to result in serious health problems for the general populace.
In recognition of such problems, there have been increasing efforts by both private environmental protection groups and governmental agencies, which taken together with increasing governmentally imposed restrictions on the disposal and use of toxic materials, to address the problem of long term, or permanent, safe storage of hazardous wastes, and to clean up existing hazardous waste sites.
Conventional long term hazardous material storage techniques include the use of sealed containers located in underground "vaults" formed in rock formations, or storage sites lined with fluid flow-"impervious" layers, such as may be formed by crushed shale or bentonite slurries. By way of example, U.S. Pat. No. 4,637,462 discloses a method of containing contaminants by injecting a bentonite/clay slurry or "mud" into boreholes in the Earth to form a barrier ring intended to limit the lateral flow of contaminants from a storage site.
Among the other prior art approaches, U.S. Pat. No. 3,934,420 discloses an approach for sealing cracks in walls of a rock chamber for storing a medium which is colder than the chamber walls. U.S. Pat. No. 2,159,954 discloses the use of bentonite to impede and control the flow of water in underground channels and pervious strata. U.S. Pat. No. 4,030,307 also discloses a liquid-"impermeable" geologic barrier, which is constructed from a compacted crushed shale. Similarly, U.S. Pat. No. 4,439,062 discloses a sealing system for an earthen container from a water expandable colloidal clay, such as bentonite.
It is also known to form storage reservoirs from frozen earthen walls disposed laterally about the material to-be-stored, such as liquified gas. See, for example, U.S. Pat. Nos. 3,267,680 and 3,183,675.
While all of such techniques do to some degree provide a limitation to the migration of materials in the Earth, none effectively provide long term, reliable containment of hazardous waste. The clay, shale and bentonite slurry and rock sealant approaches, in particular, are susceptible to failure by fracture in the event of earthquakes or other Earth movement phenomena. The frozen wall reservoir approaches do not address long term storage at all and fail to completely encompass the materials being stored. None of the prior art techniques address monitoring of the integrity of containment systems or of conditions that might lead to breach of integrity, or the correction of detected breaches of integrity.
Existing hazardous waste sites present a different problem. Many of them were constructed with little or no attempt to contain leakage; for example, municipal landfills placed in abandoned gravel pits. Furthermore, containment must either be in situ, or else the entire site must be excavated and moved. The primary current technology for in situ containment is to install slurry walls. However, that technique allows leaks under the wall; and through the wall when it cracks. Furthermore, slurry walls can only be installed successfully in a limited number of soil and rock conditions. Perhaps most importantly, there is no way to monitor when a slurry wall has been breached, nor is there any known economical means to fix such a breach.
Another practical and legislatively required factor in the provision of effective toxic material containment, is the need to be able to remove a containment system. None of the prior art systems permit economic removal of the system once it is in place.
Accordingly, it is an object of the present invention to provide an improved hazardous waste containment method and system.
Another object is to provide an improved hazardous waste containment method and system that is effective over a long term.
Yet another object is to provide an improved hazardous waste containment method and system that is economic and efficient to install and operate.
Still another object is to provide an improved hazardous waste containment method and system that may be readily removed.
It is another object to provide an improved hazardous waste containment method and system that permits integrity monitoring and correction of potential short term failures before they actually occur.
It is yet another object to provide an improved hazardous waste containment method and system that is self-healing in the event of seismic events or Earth movement.